Biometrics authentication device and portable terminal

ABSTRACT

Provided is a biometric authentication device for identifying an individual based on a biometric pattern of the subject included in a picked up image. The biometric authentication device includes: a light guiding unit for outputting light from a surface thereof; a liquid crystal display (LCD) unit for adjusting, on a display pixel basis, an intensity of light output from the surface of the light guiding unit; an image pickup unit for picking up an image of the subject; a display light source for emitting light used as a backlight of the LCD unit; a detection light source for emitting light for irradiating the subject; and a control unit for controlling processing of the biometric authentication device The control unit turns on the detection light when the image pickup unit picks up a first image, which is used for authentication, and turns on the display light source when the LCD unit displays information.

TECHNICAL FIELD

This invention relates to a biometric authentication device whichutilizes features of biometric information to identify individuals, andmore particularly, to a technology of identifying an individual based ona blood vessel pattern.

BACKGROUND ART

Biometric authentication in which features of biometric information areused to identify individuals has lately been attracting attention.Examples of biometric information include fingerprints and iris or bloodvessel patterns.

Advantages of biometric authentication are convenience and highsecurity, which are owing to the fact that biometric authentication doesnot require a person to carry a key with him/her and has less fear offraudulent acts as a consequence of the loss or theft of the key, or thelike.

Of the varying types of biometric authentication, authentication usingblood vessel patterns (blood vessel authentication) is becoming popular.Blood vessel patterns which are information within a living body aremore difficult to counterfeit than fingerprints. The security of bloodvessel authentication is accordingly higher than that of fingerprintauthentication. Further, in blood vessel authentication an eyeball doesnot need to be irradiated with light, unlike iris authentication, whichhelps users to feel less reluctant to use blood vessel authenticationand makes blood vessel authentication safe to human health.

An example of a blood vessel authentication device is disclosed in JP07-21373 A. The blood vessel authentication device irradiates a humanbody with near-infrared light. Using an image sensor, the blood vesselauthentication device takes a photograph with transmitted light andreflected light. Hemoglobin in blood absorbs near-infrared light morethan the rest of the body does, and hence a blood vessel pattern isextracted in the picked up image. The blood vessel authentication devicedetermines whether or not the blood vessel pattern extracted in thepicked up image matches any blood vessel pattern registered in advance.Based on the result of the blood vessel pattern matching, the bloodvessel authentication device identifies an individual.

In the case where a biometric authentication device is mounted to aportable electronic device such as a cellular phone, it is difficult tosecure enough space to mount a biometric authentication device in theportable electronic device. Reduction in size of biometricauthentication devices is therefore necessary.

For instance, a normal fingerprint authentication device includes acontact detection type optical image sensor, a pressure-sensitivesensor, or the like as a sensor for measuring a fingerprint pattern.These sensors have approximately the same size as the size of a humanfingertip, and are difficult to mount in a mobile electronic device. Asa solution, a fingerprint authentication device equipped with a smallline sensor has been developed. This fingerprint authentication devicephotographs a finger sliding over the small line sensor. A problem ofthe fingerprint authentication device is consequently the poor qualityof the obtained fingerprint image.

Blood vessel authentication devices, on the other hand, include an imagesensor such as a charge coupled device (CCD) sensor or a complementarymetal-oxide semiconductor (CMOS) sensor. These image sensors can bereduced in size, but a separate lens is necessary for forming an imageon the image sensor. Reducing the overall size of a blood vesselauthentication device is therefore not easy.

JP 2005-346238 A discloses a fingerprint authentication device includinga translucent image sensor overlaid on a liquid crystal display. Withthis structure, an image sensor can be disposed over a liquid crystaldisplay of a cellular phone and therefore does not require a spacededicated to the image sensor. Further, a backlight for the liquidcrystal display can be utilized, without any modifications, as anirradiation light source for photographing.

Known technologies are employable in manufacturing the translucent imagesensor. According to the known technologies, a sensor array is formed bylaminating an amorphous silicon layer or a polysilicon layer on a glasssubstrate.

DISCLOSURE OF THE INVENTION

Applying the technology disclosed in JP 2005-346238 A to a blood vesselauthentication device raises the following problems:

Firstly, in blood vessel authentication devices where infrared light isused as irradiation light, the backlight of a liquid crystal displaycannot be used as the irradiation light source. Blood vesselauthentication devices therefore need to include a separate infraredlight source on the periphery of the liquid crystal display. Then, theproblem of insufficient intensity of light arises in a central part ofthe liquid crystal display which is distant from the infrared lightsource.

Secondly, in blood vessel authentication devices, the relativepositional relation between the light source and a subject is easilychanged depending on where the subject is placed. This leads to theproblem of unstable intensity of light distribution in a picked upimage.

Further, even if a liquid crystal backlight is somehow made usable asthe irradiation light source, blood vessel authentication devicesundesirably allow scattered light that is generated when irradiationlight is transmitted through the substrate of the translucent sensor tointrude in a picked up image. The quantum noise of scattered lightcauses lowering in contrast-to-noise ratio of a picked up image andaccordingly degrades the image quality of the picked up image.

The effect of image quality degradation due to the quantum noise ofscattered light is particularly large in blood vessel authenticationdevices where the intensity of signal light that is output from theliving body is very low compared with that of the irradiation light.

Those various problems mentioned above lower the authentication accuracyof a biometric authentication device. An object of a representative modeof this invention is therefore to provide a biometric authenticationdevice that has high authentication accuracy.

According to the representative mode of this invention, a biometricauthentication device for identifying an individual who is associatedwith a subject based on a biometric pattern of the subject which isincluded in a picked up image, includes: a light guiding unit foroutputting, from a surface thereof, light incident on an end facethereof; a liquid crystal display unit for adjusting, on a display pixelbasis, an intensity of light output from the surface of the lightguiding unit, and then outputting the light in a direction of thesubject; an image pickup unit for picking up an image of the subject; adisplay light source for emitting light used as a backlight of theliquid crystal display unit such that the light is incident on the endface of the light guiding unit; a detection light source for emittinglight for irradiating the subject such that the light is incident on theend face of the light guiding unit; and a control unit for controllingprocessing of the biometric authentication device, in which: the controlunit turns on the detection light when the image pickup unit picks up afirst image, which is used for authentication; and the control unitturns on the display light source when the liquid crystal display devicedisplays information.

According to the representative mode of this invention, the biometricauthentication device can be enhanced in authentication accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of a biometric authentication device inaccordance with a first embodiment of this invention.

FIG. 2 is an explanatory diagram of an external appearance of a cellularphone on which a biometric authentication device is installed inaccordance with the first embodiment of this invention.

FIG. 3 is an explanatory diagram of placement of a subject put on thebiometric authentication device in accordance with the first embodimentof this invention.

FIG. 4 is an explanatory diagram of a mask image which is displayed onthe biometric authentication device when the subject is photographed inaccordance with the first embodiment of this invention.

FIG. 5 is a sectional view of the biometric authentication device inaccordance with the first embodiment of this invention.

FIG. 6 is an explanatory diagram of another mask image which isdisplayed on the biometric authentication device when the subject isphotographed in accordance with the first embodiment of this invention.

FIG. 7 is a flow chart of authentication processing that is executed bythe biometric authentication device in accordance with the firstembodiment of this invention.

FIG. 8 is an explanatory diagram of a first guide screen image which isdisplayed on the biometric authentication device at the start ofauthentication in accordance with the first embodiment of thisinvention.

FIG. 9 is an explanatory diagram of a second guide screen image which isdisplayed on the biometric authentication device when authenticationfails in accordance with the first embodiment of this invention.

FIG. 10 is an explanatory diagram of a third guide screen image which isdisplayed on the biometric authentication device when authenticationsucceeds in accordance with the first embodiment of this invention.

FIG. 11 is a flow chart of a mask image creating processing inaccordance with the first embodiment of this invention.

FIG. 12 is a flow chart of a display gray scale setting processing inaccordance with the first embodiment of this invention.

FIG. 13 is an explanatory diagram of an arrangement of a display LED anda detection LED in accordance with the first embodiment of thisinvention.

FIG. 14 is an explanatory diagram of an arrangement of a display LED anda detection LED in accordance with the first embodiment of thisinvention.

FIG. 15 is an explanatory diagram of an arrangement of adisplay/detection LED in accordance with the first embodiment of thisinvention.

FIG. 16 is a top view of a sensor board that is provided in thebiometric authentication device in accordance with the first embodimentof this invention.

FIG. 17 is a side view in section of the sensor board that is providedin the biometric authentication device in accordance with the firstembodiment of this invention.

FIG. 18 is an explanatory diagram of an actual shooting mask image A,which is displayed on the biometric authentication device in first-timeactual shooting in accordance with a second embodiment of thisinvention.

FIG. 19 is an explanatory diagram of an actual shooting mask image B,which is displayed on the biometric authentication device in second-timeactual shooting in accordance with the second embodiment of thisinvention.

FIG. 20 is an explanatory diagram of positional relation between anactual shooting mask image A and an actual shooting mask image B inaccordance with the second embodiment of this invention.

FIG. 21 is a flow chart of authentication processing that is executed bythe biometric authentication device in accordance with the secondembodiment of this invention.

FIG. 22 is a flow chart of the actual shooting mask image creatingprocessing in accordance with the second embodiment of this invention.

FIG. 23 is an explanatory diagram of a transmissive mask image, which isdisplayed on the biometric authentication device when the subject isphotographed in accordance with a third embodiment of this invention.

FIG. 24 is a flow chart of authentication processing that is executed bythe biometric authentication device in accordance with the thirdembodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of this invention will be described below with reference tothe drawings.

First Embodiment

FIG. 1 is a structural diagram of a biometric authentication deviceaccording to a first embodiment of this invention.

The biometric authentication device performs authentication based on thepattern of blood vessels 2 of a subject 1. The subject 1 is a humanfinger in this embodiment, but may be other body parts than a finger aslong as the pattern of the blood vessels 2 can be photographed. Examplesof other body parts than a finger include the palm of a hand and theback of a hand.

In this embodiment, the width direction of the subject 1 is an X axis,the longitudinal direction of the subject 1 is a Y axis, and a directionperpendicular to an input face of the biometric authentication device isa Z axis.

The biometric authentication device includes a grid 3, a sensor board 4,a liquid crystal display board 5, an optical waveguide 6, a displaylight emission diode (LED) 7, a detection LED 8, a support frame 9,electrodes 10A and 10B, a shooting control device CTL, a detected imagememory MEM1, a display image memory MEM2, a central processing unit CPU,and a speaker SPK.

The biometric authentication device can be mounted on another devicesuch as a cellular phone. In this case, parts of the device on which thebiometric authentication device is mounted may be used as some or all ofthe detected image memory MEM1, the display image memory MEM2, thecentral processing unit CPU, and the speaker SPK.

The display LED 7, which is placed on the root side of the subject 1 inthis explanatory diagram, may be set on the tip side of the subject 1.The detection LED 8, which is placed on the tip side of the subject 1 inthis explanatory diagram, may be set on the root side of the subject 1.The display LED 7 and the detection LED 8 are fixed by the support frame9. The placement of the display LED 7 and the detection LED 8 isdescribed in detail with reference to FIGS. 13, 14, and 15.

The optical waveguide 6, the liquid crystal display board 5, the sensorboard 4, and the grid 3 are overlaid in the Z axis direction in thestated order. The optical waveguide 6, the liquid crystal display board5, the sensor board 4, and the grid 3 are fixed by the support frame 9.

A top face of the support frame 9 is positioned to be on a higher levelthan a top face of the grid 3. This way, a pressure to the blood vessels2 from the contact between the subject 1 and the grid 3 is prevented asmuch as possible, whereby an image containing a clear pattern of theblood vessels 2 is picked up. The electrodes 10A and 10B are placed onthe top face of the support frame 9.

Functions of the components constituting the biometric authenticationdevice are described next.

The display LED 7 is a known LED light source and emits white light. Thedisplay LED 7 is used as a backlight when the liquid crystal displayboard 5 displays various types of information. The display LED 7 mayalso be used for irradiation light with which a subject is irradiated.

The detection LED 8 is a known LED light source and emits infraredlight. The detection LED 8 is therefore used to emit irradiation lightwith which a subject is irradiated in biometric authentication. When thedisplay LED 7 and the detection LED 8 are to emit irradiation light willbe described later with reference to FIGS. 7, 11, and 12.

The optical waveguide 6 diffuses light emitted from the display LED 7 orthe detection LED 8 in an X-Y plane direction in a uniform manner tooutput diffused light in the Z axis direction. The optical waveguide 6is a known optical waveguide that is employed in liquid crystal displaysand the like.

The liquid crystal display board 5 includes a thin film transistor (TFT)drive substrate, a polarizing filter, a transparent electrode, a liquidcrystal layer, a color filter, and others. The color filter employed isa type that is transmissive of infrared light emitted from the detectionLED 8, in addition to being transmissive of light of R, G, and B colors.In the liquid crystal display board 5, the intensity of transmittedlight of the liquid crystal layer is controlled on a display pixel basisby controlling a voltage applied to the liquid crystal layer. The liquidcrystal display board 5 employed is a known liquid crystal display boardwhich has a plurality of display pixels.

The liquid crystal display board 5 has a mask function, a lightadjustment function, and a display function. The mask function is forcontrolling a region that transmits infrared light output from theoptical waveguide 6 (irradiation region) and a region that does nottransmit infrared light output from the optical waveguide 6 (maskregion). The light adjustment function is for adjusting the intensity ofinfrared light that is transmitted after output from the opticalwaveguide 6. The display function is for displaying various types ofinformation including text and images.

The sensor board 4 is a translucent substrate and transmits light suchthat part of light entering from a bottom face of the sensor board 4exits a top face of the sensor board 4. The sensor board 4 picks up animage by detecting only light that enters from the top face. Forexample, a known photodiode array that is formed by laminating amorphoussilicon on a glass substrate is used as the sensor board 4. Details ofthe structure of the sensor board 4 will be described later withreference to FIGS. 16 and 17.

The grid 3 has many minute grid cells formed inside, which enables thegrid 3 to block incident light that is oblique with respect to the planeof the board of the grid 3. For example, a known lattice grid for use inan anti-peep filter (privacy filter) is employed as the grid 3.

The grid 3 controls the incident angle range of light that is incidenton the subject 1. The grid 3 thus prevents the light irradiation regionwhich is controlled by the mask function of the liquid crystal displayboard 5 from expanding.

The grid 3 also controls the output angle of light output from thesubject 1. An image containing the pattern of the blood vessels 2 isthus formed on the sensor board 4. Further, the grid 3 preventsscattered light from degrading the image quality.

The electrodes 10A and 10B are used to detect that the subject 1 is puton the biometric authentication device. Specifically, a power source(omitted from the drawing) provides a slight electric potentialdifference between the electrode 10A and the electrode 10B. At themoment when the subject 1 is put in place, a current flows between theelectrode 10A and the electrode 10B via the subject 1. The biometricauthentication device detects that the subject 1 has been put in placeby measuring a current that flows between the electrodes 10A and 10B.

The shooting control device CTL controls the turning on/off of thedisplay LED 7 and the detection LED 8 following instructions from thecentral processing unit CPU. The shooting control device CTL reads imagedata recorded in the display image memory MEM2, and displays the readimage data on the liquid crystal display board 5. The shooting controldevice CTL also controls the picking up of an image by the sensor board4.

The detected image memory MEM1 records an image picked up by the sensorboard 4.

The central processing unit CPU performs various types of processing.For example, from an image recorded in the detected image memory MEM1,the central processing unit CPU creates an image to be displayed on theliquid crystal display board 5 by a method described later withreference to FIG. 11. The central processing unit CPU next records thecreated image in the display image memory MEM2.

The central processing unit CPU also executes biometric authenticationof the subject 1 based on an image that is recorded in the detectedimage memory MEM1. For example, the central processing unit CPU uses atechnology disclosed in JP 07-21373 A to execute biometricauthentication of the subject 1.

The result of biometric authentication executed by the centralprocessing unit CPU is output from at least one of the liquid crystaldisplay board 5 and the speaker SPK. The biometric authentication devicethus notifies a user of the result of biometric authentication.

Described next is a path of infrared light 11 with which an imagecontaining the pattern of the blood vessels 2 is formed.

The infrared light 11 emitted from the detection LED 8 is firstscattered inside the optical waveguide 6 and output in a directiontoward a top face of the optical waveguide 6. The infrared light 11 isnext transmitted through the liquid crystal display board 5, the sensorboard 4, and the grid 3, and then enters the subject 1. The infraredlight 11 is scattered inside the subject 1 and transmitted through theblood vessels 2. Thereafter, the infrared light 11 is output from thesubject 1. The infrared light 11 is next transmitted through the grid 3and then enters the sensor board 4, which detects the infrared light 11upon incidence.

Part of the infrared light 11 is blocked by the mask function or lightadjustment function of the liquid crystal display board 5. Whentransmitted through the sensor board 4, the infrared light 11 ispartially blocked or scattered. The infrared light 11 that entersobliquely with respect to the plane of the board of the grid 3 isblocked by the grid 3.

FIG. 2 is an explanatory diagram of the external appearance of acellular phone 20 on which a biometric authentication device 21 isinstalled according to the first embodiment of this invention.

The cellular phone 20 is of a folding type, and includes a main displayand a sub-display. The cellular phone 20 may not be foldable and mayinstead be one piece. The biometric authentication device 21 in thisexplanatory diagram uses the sub-display of the cellular phone 20, butmay use the main display.

A start switch 22 and the electrodes 10A and 10B are disposed in anouter casing of the cellular phone 20.

The electrodes 10A and 10B are used to detect that the subject 1 is puton the biometric authentication device 21. The electrodes 10A and 10Bare therefore located around the sub-display of the cellular phone 20.The start switch 22 receives an instruction to start biometricauthentication from a user.

FIG. 3 is an explanatory diagram of how the subject 1 is put on thebiometric authentication device 21 according to the first embodiment ofthis invention.

A user places the subject 1 such that the subject 1 comes into contactwith the two electrodes 10A and 10B simultaneously. However, theplacement location of the subject 1 varies each time authentication isexecuted. The biometric authentication device 21 of this embodiment iscapable of picking up an image that contains a clear pattern of theblood vessels 2 irrespective of how the subject 1 is placed.

This embodiment takes as an example a case in which the subject 1 is thethumb of the right hand, but the subject 1 may be other fingers of theright hand or a finger of the left hand.

FIG. 4 is an explanatory diagram of a mask image which is displayed onthe biometric authentication device 21 when the subject 1 isphotographed according to the first embodiment of this invention.

When photographing the subject 1, the biometric authentication device 21creates a mask image based on the shape and placement location of thesubject 1. The biometric authentication device 21 then displays thecreated mask image.

The mask image contains a mask region 42 and an irradiation region 41.The mask region 42 is a region that is displayed black by the liquidcrystal on the display screen. In other words, the mask region 42 is aregion in which infrared light output from the optical waveguide 6 isnot transmitted and accordingly the subject 1 is not irradiated withlight. The irradiation region 41, on the other hand, is a region inwhich the subject 1 is irradiated with light, and corresponds to otherregions than the mask region 42.

The mask region 42 is a region slightly inside an outline 40 of thesubject 1 viewed from the Z axis direction.

In the mask region 42, infrared light output from the optical waveguide6 is blocked by cells displaying black of liquid crystal. The infraredlight output from the optical waveguide 6 therefore irradiates thesubject 1 only in an outline region 43 out of the irradiation region 41.The outline region 43 is a gap between a region inside the outline ofthe subject 1 and the mask region 42.

In this way, the biometric authentication device 21 irradiates thesubject 1 with always the same infrared rays regardless of a change inhow the subject 1 is put on the biometric authentication device 21. Thebiometric authentication device 21 can thus pick up an image containinga clear pattern of the blood vessels 2 stably.

FIG. 5 is a sectional view of the biometric authentication device 21according to the first embodiment of this invention.

The biometric authentication device 21 of FIG. 5 is displaying a maskimage containing the irradiation region 41 and the mask region 42. Theirradiation region 41 contains the outline region 43.

Of infrared light output from the optical waveguide 6, infrared lightthat is output from below the mask region 42 is blocked by liquidcrystal molecules aligned to display black, and therefore does not enterthe subject 1.

If infrared light is transmitted in the mask region 42, part of infraredlight output from the optical waveguide 6 is scattered by protectiveglass (omitted from the drawing) disposed on a top face of the sensorboard 4 or by a bottom face of the grid 3. Scattered light such as thisenters the sensor board 4 and degrades the image quality of the pickedup image. For instance, scattered light narrows the dynamic range of thesensor board 4. Moreover, the quantum noise of scattered light causeslowering in the contrast-to-noise ratio of a picked up image.

The biometric authentication device 21 of this embodiment prevents imagequality degradation due to scattered light by displaying a mask image.

Of infrared light output from the optical waveguide 6, infrared lightthat is output from below the outline region 43 is transmitted throughthe liquid crystal display board 5 and enters the subject 1, therebycontributing to the formation of an image that contains the pattern ofthe blood vessels 2. The biometric authentication device 21 adjusts theintensity of light with which the subject 1 is irradiated to anappropriate value. For that purpose, the biometric authentication device21 adjusts the liquid crystal gray scale of the irradiation region 41 bya method described later with reference to FIG. 12.

FIG. 6 is an explanatory diagram of another mask image which isdisplayed on the biometric authentication device 21 when the subject 1is photographed according to the first embodiment of this invention.

When photographing the subject 1, the biometric authentication device 21may display the mask image illustrated in FIG. 6 instead of the maskimage illustrated in FIG. 4. In the mask image illustrated in FIG. 6,the outline region 43 alone is set as the irradiation region and otherregions than the outline region 43 are set as the mask region.

The biometric authentication device 21 blocks infrared light that straysinto the central part of the subject 1 through reflection or scatteringby displaying the mask image of FIG. 6. The biometric authenticationdevice 21 can thus improve the image quality of a picked up image evenmore.

FIG. 7 is a flow chart of authentication processing that is executed bythe biometric authentication device 21 according to the first embodimentof this invention.

Steps shown in broken line in this flow chart indicate screen imagesdisplayed on the liquid crystal display board 5. The screen imagedisplayed on the liquid crystal display board 5 is kept displayed untilit is changed to the next screen image.

First, the biometric authentication device 21 stands by until the startswitch 22 is operated (S1). Nothing is displayed on the liquid crystaldisplay board 5 at this point (S12). The display LED 7 and the detectionLED 8 are accordingly not lit.

When the start switch 22 is subsequently operated (S2), the biometricauthentication device 21 applies a voltage between the electrode 10A andthe electrode 10B (S3). At this point, the biometric authenticationdevice 21 displays a first guide screen image illustrated in FIG. 8 onthe liquid crystal display board 5 (S13). The biometric authenticationdevice 21 lights the display LED 7 alone in accordance with what isdisplayed in the first guide screen image. In other words, the detectionLED 8 is kept off.

FIG. 8 is an explanatory diagram of the first guide screen image whichis displayed on the biometric authentication device 21 at the start ofauthentication according to the first embodiment of this invention.

The biometric authentication device 21 instructs a user to put thesubject 1 in place by displaying the first guide screen image. The firstguide screen image may show where to place the subject 1. This way, thepositioning accuracy of the subject 1 is improved and themisidentification ratio of biometric authentication by the biometricauthentication device 21 is accordingly lowered.

The description now returns to FIG. 7.

After applying a voltage between the electrodes 10A and 10B, thebiometric authentication device 21 measures a current value between theelectrodes 10A and 10B (S4). The biometric authentication device 21 nextdetermines from the measured current value whether or not the placing ofthe subject 1 has been detected (S6).

When the placing of the subject 1 has not been detected, the biometricauthentication device 21 determines whether or not a given period oftime has elapsed since the start switch 22 was operated. The givenperiod of time is, for example, 30 seconds (S5).

When it is determined that the given period of time has elapsed, thebiometric authentication device 21 returns to Step S1 to stand by.

When it is determined that the given period of time has not beenelapsed, on the other hand, the biometric authentication device 21returns to Step S4, where a current value between the electrodes 10A and10B is measured again.

When the placing of the subject 1 has been detected in Step S6, thebiometric authentication device 21 executes mask image creatingprocessing (S7). In the mask image creating processing, the biometricauthentication device 21 extracts the outline 40 of the subject 1 and,from the extracted outline 40, creates the mask image illustrated inFIG. 4 or FIG. 6. Details of the mask image creating processing will bedescribed with reference to FIG. 11.

The biometric authentication device 21 displays the created mask imageon the liquid crystal display board 5 (S14). As the mask image isdisplayed, the biometric authentication device 21 turns the display LED7 off and turns the detection LED 8 on.

The biometric authentication device 21 next performs display gray scalesetting processing (S8). Through this processing, the biometricauthentication device 21 adjusts the liquid crystal gray scale of theirradiation region 41. Details of the display gray scale settingprocessing will be described with reference to FIG. 12.

The biometric authentication device 21 then executes actual shooting(S9). Through the actual shooting, the biometric authentication device21 picks up an image that contains the pattern of the blood vessels 2.

The biometric authentication device 21 performs authentication based onthe image picked up through the actual shooting (S10). The biometricauthentication device 21 then determines whether or not theauthentication has succeeded (S11).

When the authentication has failed, the biometric authentication device21 returns to Step S4 to repeat the processing. At this point, thebiometric authentication device 21 displays a second guide screen imageillustrated in FIG. 9 on the liquid crystal display board 5 (S15). Asthe second guide screen image is displayed, the biometric authenticationdevice 21 turns the display LED 7 on and turns the detection LED 8 off.The biometric authentication device 21 simultaneously sounds an alarm ina manner different from the one used to notify a success ofauthentication, for example, by making a beeping sound twice, in orderto notify the user of authentication failure. The user can thus know ofauthentication failure while keeping the finger put on the biometricauthentication device 21.

FIG. 9 is an explanatory diagram of the second guide screen image whichis displayed on the biometric authentication device 21 whenauthentication fails according to the first embodiment of thisinvention.

The biometric authentication device 21 notifies the user ofauthentication failure and instructs the user to put the subject 1 inplace by displaying the second guide screen image. The second guidescreen image may show where to place the subject 1.

The description now returns to FIG. 7.

In the case where the authentication succeeds in Step S11, the biometricauthentication device 21 displays a third guide screen image illustratedin FIG. 10 on the liquid crystal display board 5 (S16). As the thirdguide screen image is displayed, the biometric authentication device 21turns the display LED 7 on and turns the detection LED 8 off. Thebiometric authentication device 21 simultaneously sounds an alarm in amanner different from the one used to notify a failure ofauthentication, for example, by making a beeping sound once, in order tonotify the user of authentication success. The user can thus know ofauthentication success while keeping the finger put on the biometricauthentication device 21.

The biometric authentication device 21 then ends the authenticationprocessing.

FIG. 10 is an explanatory diagram of the third guide screen image whichis displayed on the biometric authentication device 21 whenauthentication succeeds according to the first embodiment of thisinvention.

The biometric authentication device 21 notifies the user ofauthentication success by displaying the third guide screen image. Thethird guide screen image may display the identifier or the like of thesuccessfully authenticated user.

FIG. 11 is a flow chart of the mask image creating processing accordingto the first embodiment of this invention.

Steps shown in broken line in this flow chart indicate screen imagesdisplayed on the liquid crystal display board 5. The screen imagedisplayed on the liquid crystal display board 5 is kept displayed untilit is changed to the next screen image.

The mask image creating processing is executed in Step S7 of theauthentication processing (FIG. 7).

In the case where the placing of the subject 1 is detected in Step S6 ofthe authentication processing (FIG. 7), the biometric authenticationdevice 21 prepares for first-time preliminary shooting (T1). Thebiometric authentication device 21 here displays on the liquid crystaldisplay board 5 a screen image that contains no other region than theirradiation region (T10). At this point, the biometric authenticationdevice 21 turns off the display LED 7 and the detection LED 8. Thebiometric authentication device 21 then executes the first-timepreliminary shooting (T2).

The biometric authentication device 21 next prepares for second-timepreliminary shooting (T3). The biometric authentication device 21 herekeeps the screen image that contains no other region than theirradiation region displayed on the liquid crystal display board 5(T11). The biometric authentication device 21 also lights at least oneof the display LED 7 and the detection LED 8. The biometricauthentication device 21 then executes the second-time preliminaryshooting (T4).

The biometric authentication device 21 creates a differential image froman image obtained through the first-time preliminary shooting and animage obtained through the second-time preliminary shooting (T5).Specifically, the biometric authentication device 21 subtracts, for eachpixel, the pixel value of the image obtained through the first-timepreliminary shooting from the pixel value of the image obtained throughthe second-time preliminary shooting.

The created differential image is an image ridded of external lightcomponents incident on a region where the subject 1 is not placed (aregion outside the outline 40 of the subject 1). In other words, thecreated differential image is solely of the region inside the outline 40of the subject 1.

Therefore, the biometric authentication device 21 can accurately detectthe placement location of the subject 1 by referring to the createddifferential image, irrespective of the state of external light.

The biometric authentication device 21 next creates a histogram of pixelvalues in the created differential image (T6). From the createdhistogram, the biometric authentication device 21 calculates a meanmaximum value P_(max) and mean minimum value P_(min) of the pixel values(T7).

For example, the mean maximum value P_(max) is an average of the pixelvalues of pixels that belong to the top 10% of the histogram out of allthe pixels contained in the differential image. The mean minimum valueP_(min) is an average of the pixel values of pixels that belong to thebottom 10% of the histogram out of all the pixels contained in thedifferential image.

The biometric authentication device 21 may use a maximum sum pixel valueand a minimum sum pixel value instead of the mean maximum value P_(max)and the mean minimum value P_(min). The maximum sum pixel value is themaximum value of the sum of pixel values that a given number of adjacentpixels (e.g., four adjacent pixels) take. The minimum sum pixel value isthe minimum value of the sum of pixel values that the given number ofadjacent pixels take.

The biometric authentication device 21 next uses the followingMathematical Expression (1) to calculate a threshold P_(t), which is fordiscriminating the mask region 42 and the irradiation region 41 fromeach other (T8):P _(t) =P _(min) +αP _(max) −P _(min))  (1)α is a parameter for determining the threshold P_(t), and is set inadvance. The mask region 42 shrinks as α approaches “0” (as α becomessmaller). The mask region expands as α approaches “1” (as α becomeslarger). A typical value of α is “0.2”.

Based on the calculated threshold P_(t), the biometric authenticationdevice 21 creates the mask image illustrated in FIG. 4 (T9). In thecreated mask image, a pixel that has a pixel value equal to or largerthan the threshold P_(t) constitutes the mask region 42. A pixel thathas a pixel value smaller than the threshold P_(t) constitutes theirradiation region 41.

The biometric authentication device 21 then ends the mask image creatingprocessing.

The biometric authentication device 21 in this example creates the maskimage illustrated in FIG. 4. The biometric authentication device 21 cancreate the mask image illustrated in FIG. 6 through processing describedbelow.

The biometric authentication device 21 uses the following MathematicalExpressions (2) and (3) in Step T8 to calculate thresholds P_(t1) andP_(t2), which are for discriminating the mask region 42 and theirradiation region 41 from each other (T8):P _(t1) =P _(min)+α₁(P _(max) −P _(min))  (2)P _(t2) =P _(min)+α₂(P _(max)−_(min))  (3)α₁ is a parameter for determining the threshold P_(t1), and is set inadvance. α₂ is a parameter for determining the threshold P_(t2), and isset in advance. Here, α₁ is larger than α₂. A typical value of α₁ is“0.2” and a typical value of α₂ is “0.05”.

Based on the calculated thresholds P_(t1) and P_(t2), the biometricauthentication device 21 creates the mask image illustrated in FIG. 6(T9). In the created mask image, a pixel that has a pixel value equal toor smaller than the threshold P_(t2) and a pixel that has a pixel valueequal to or larger than the threshold P_(t1) constitute the mask region42. A pixel that has a pixel value larger than the threshold P_(t2) andsmaller than the threshold P_(t1) constitutes the irradiation region 41.

The biometric authentication device 21 creates the mask imageillustrated in FIG. 6 in this manner.

FIG. 12 is a flow chart of the display gray scale setting processingaccording to the first embodiment of this invention.

Steps shown in broken line in this flow chart indicate screen imagesdisplayed on the liquid crystal display board 5. The screen imagedisplayed on the liquid crystal display board 5 is kept displayed untilit is changed to the next screen image.

The display gray scale setting processing is executed in Step S8 of theauthentication processing (FIG. 7).

First, the biometric authentication device 21 prepares for third-timepreliminary shooting (U1). The biometric authentication device 21 heredisplays on the liquid crystal display board 5 a mask image created inStep S7 of the authentication processing (U7). The liquid crystal grayscale of the irradiation region 41 contained in the displayed mask imageis set to an initial value D₀. At this point, the biometricauthentication device 21 turns off the display LED 7 alone. In otherwords, the detection LED 8 is kept lit. The biometric authenticationdevice 21 then executes the third-time preliminary shooting (U2).

From an image obtained through the third-time preliminary shooting, thebiometric authentication device 21 extracts pixels that correspond tothe mask region 42 contained in the displayed mask image. Based on thepixel values of the extracted pixels which correspond to the mask region42, the biometric authentication device 21 creates a histogram of pixelvalues in the image obtained through the third-time preliminary shooting(U6). In short, this histogram is solely about pixels that correspond tothe mask region 42.

The biometric authentication device 21 calculates from the createdhistogram a mean maximum value P_(max) of the pixel values (U4). Themean maximum value P_(max) is, for example, an average of the pixelvalues of pixels that belong to the top 10% of the histogram out of allthe pixels that correspond to the mask region 42.

The biometric authentication device 21 next uses the followingMathematical Expression (4) to calculate a liquid crystal gray scale Dof the irradiation region 41 in the actual shooting (U5):D=D ₀ ×P _(max) /P ₀  (4)

P₀ represents an objective value for the mean maximum value of pixelvalues in an image obtained through the actual shooting, and is set inadvance.

Next, the biometric authentication device 21 prepares for the actualshooting (U6). The biometric authentication device 21 here displays amask image created in Step S7 of the authentication processing on theliquid crystal display board 5 (U8). The liquid crystal gray scale Dcalculated in Step U5 is set to the irradiation region 41 of thedisplayed mask image. At this point, the biometric authentication device21 keeps the display LED 7 turned off and keeps the detection LED 8 lit.The biometric authentication device 21 then ends the display gray scalesetting processing.

By setting the calculated liquid crystal gray scale D to the irradiationregion 41 of the mask image, the biometric authentication device 21 canset the mean maximum value of pixel values in the image obtained throughthe actual shooting to P₀. In other words, the biometric authenticationdevice 21 prevents overexposure and underexposure by optimizing theintensity of light with which the subject 1 is irradiated in the actualshooting.

FIG. 13 is an explanatory diagram of the arrangement of the display LED7 and the detection LED 8 according to the first embodiment of thisinvention.

In this explanatory diagram, the display LED 7 and the detection LED 8are placed on sides that face the optical waveguide 6, with the displayLED 7 above the optical waveguide 6 and the detection LED 8 below theoptical waveguide 6. This arrangement may be reversed. The display LED 7may also be placed on one of the right side and the left side while thedetection LED 8 is placed on the other of the right side and the leftside.

While one display LED 7 and one detection LED 8 are disposed in thisexplanatory diagram, there may be a plurality of display LEDs 7 and aplurality of detection LEDs 8.

FIG. 14 is an explanatory diagram of the arrangement of the display LED7 and the detection LED 8 according to the first embodiment of thisinvention.

In this explanatory diagram, the display LED 7 and the detection LED 8are placed on the same side with respect to the optical waveguide 6,specifically, below the optical waveguide 6. The display LED 7 and thedetection LED 8 may instead be placed above, to the right, or to theleft of the optical waveguide 6.

The display LED 7 and the detection LED 8 may also be placed both aboveand below the optical waveguide 6. This way, unevenness in intensity oflight is reduced in a top-bottom direction of the optical waveguide 6.Similarly, the display LED 7 and the detection LED 8 may be placed bothto the right and left of the optical waveguide 6.

While one display LED 7 is disposed in this explanatory diagram, theremay be a plurality of display LEDs 7. While two detection LEDs 8 aredisposed in this explanatory diagram, there may be any number ofdetection LEDs 8.

As described above, in the biometric authentication device 21 of thisembodiment, the display LED 7 and the detection LED 8 are placed so asto share the same optical waveguide 6. The biometric authenticationdevice 21 can thus be reduced in size.

FIG. 15 is an explanatory diagram of the arrangement of adisplay/detection LED 150 according to the first embodiment of thisinvention.

The biometric authentication device 21 may include the display/detectionLED 150 instead of the display LED 7 and the detection LED 8. Then, thesize of the biometric authentication device 21 can be reduced evenfurther. The display/detection LED 150 includes a white light source fordisplay use and an infrared light source for detection use.

In this explanatory diagram, the display/detection LEDs 150 are placedbelow the optical waveguide 6. Alternatively, the display/detection LEDs150 may be placed above, to the right, or to the left of the opticalwaveguide 6. The display/detection LEDs 150 may also be placed bothabove and below the optical waveguide 6. Similarly, thedisplay/detection LEDs 150 may be placed both to the right and left ofthe optical waveguide 6.

While two display/detection LEDs 150 are disposed in this explanatorydiagram, there may be any number of display/detection LEDs 150.

FIG. 16 is a top view of the sensor board 4 that is provided in thebiometric authentication device 21 according to the first embodiment ofthis invention.

The sensor board 4 includes photodiodes 160, light transmissive regions161, thin film transistor (TFT) switches 162, a shift register 163, asignal reading circuit 164, gate lines 165, data lines 166, and others.

The photodiodes 160, the TFT switches 162, the shift register 163, thegate lines 165, and the data lines 166 are formed on a glass substrate(omitted from the drawing). These are formed with the use of a knowntechnology of laminating amorphous silicon or polysilicon on a glasssubstrate.

The light transmissive regions 161 are regions that transmit white lightemitted from the display LED 7 and infrared light emitted from thedetection LED 8.

The gate lines 165 couple the shift register 163 to gates of the TFTswitches 162. The gate lines 165 are used to supply a voltage to thegates of the TFT switches 162.

The photodiodes 160 are coupled to one end of the data lines 166 via theTFT switches 162. The other end of the data lines 166 are coupled to thesignal reading circuit 164. The data lines 166 are used to read chargesignals from the photodiodes 160.

The signal reading circuit 164 is formed on a single crystal siliconsubstrate by a known CMOS process or the like.

The signal reading circuit 164 includes charge amplifiers 167, amultiplexer 168, an A/D converter 169, and others.

The data lines 166 formed on a glass substrate and the signal readingcircuit 164 formed on a single crystal silicon substrate areelectrically coupled to each other by a bonding wire (omitted from thedrawing).

Part of light output from below the sensor board 4 is transmittedthrough the light transmissive regions 161 and output to a space abovethe sensor board 4. Part of light entering from above the sensor board 4is converted into charge signals by the photodiodes 160. In the casewhere the TFT switches 162 are shut off, the charge signals obtained bythe conversion are accumulated in junctions of the photodiodes 160. Whenthe TFT switches 162 are turned on, the charge signals accumulated inthe junctions of the photodiodes 160 are sent to the charge amplifiers167 via the data lines 166.

The charge amplifiers 167 integrate the received charge signals andoutput voltage signals which are generated by the integration to the A/Dconverter 169. The A/D converter 169 converts the signals input from thecharge amplifiers 167 into digital signals. The A/D converter 169 storesthe digital signals obtained by the conversion in the detected imagememory MEM1. In the manner described above, the detected image memoryMEM1 stores an image picked up by the sensor board 4.

The shift register 163, on the other hand, supplies a voltage to thegates of the TFT switches 162 via the gate lines 165. The shift register163 thus turns the TFT switches 162 on and off. The shift register 163supplies a voltage to the gate lines 165 sequentially, moving from onegate line 165 to another along the Y axis direction.

The multiplexer 168 selects the charge amplifiers 167 sequentially alongthe X axis direction as a charge amplifier that outputs signals to theA/D converter 169.

FIG. 17 is a side view in section of the sensor board 4 that is providedin the biometric authentication device 21 according to the firstembodiment of this invention.

This explanatory diagram is a side view in section at a point Fillustrated in FIG. 16.

The sensor board 4 includes a glass substrate 170, an insulating film171, a drain electrode 172, an n-type layer 173, an i-type layer 174, ap-type layer 175, a transparent electrode 176, a lower light shieldingfilm 177, a gate electrode 178, a source electrode 179, a semiconductorfilm 180, an upper light shielding film 181, a protective glass 182, aninterlayer film 183, and others.

The protective glass 182 is placed on top of the sensor board 4 toprotect the interior of the sensor board 4. The semiconductor film 180,the drain electrode 172, the gate electrode 178, and the sourceelectrode 179 constitute each TFT switch 162.

The n-type layer 173, the i-type layer 174, and the p-type layer 175constitute each photodiode 160. The n-type layer 173, the i-type layer174, and the p-type layer 175 are each formed from amorphous siliconthat is small in leak current.

The transparent electrode 176 is formed from a known material such asindium tin oxide (ITO). Part of light entering from above the sensorboard 4 is transmitted through the transparent electrode 176 and entersthe photodiodes 160.

The drain electrode 172 serves both as the drain electrode of the TFTswitch 162 and as an electrode of the photodiode 160 that is on the sideof the n-type layer 173, and couples the photodiode 160 and the TFTswitch 162 to each other. The drain electrode 172 is formed so as tocover the entire bottom face of the photodiode 160. Light entering thephotodiode 160 from below the sensor board 4 is thus blocked. The drainelectrode 172 is formed from aluminum, chromium, or the like.

The lower light shielding film 177 and the upper light shielding film181 are formed from a known light shielding material. The lower lightshielding film 177 blocks light that enters the TFT switch 162 frombelow the sensor board 4. The upper light shielding film 181 blockslight that enters the TFT switch 162 from above the sensor board 4.These light shielding films prevent a malfunction of the TFT switch 162due to photoelectric effects.

As has been described, in the biometric authentication device 21 of thisembodiment, the sensor board 4 for biometric authentication is placed ona liquid crystal display that is mounted to a cellular phone or thelike. The biometric authentication device 21 irradiates the subject 1uniformly with infrared light, utilizing the optical waveguide 6 whichis used in a backlight of the liquid crystal display. The biometricauthentication device 21 can thus obtain a picked up image in which thelight intensity distribution is stable regardless of variations in wherethe subject 1 is placed.

Further, the biometric authentication device 21 of this embodimentcontrols the infrared light irradiation range and irradiation lightintensity by displaying a mask image on the liquid crystal display. Thebiometric authentication device 21 can therefore pick up an image havinga high contrast-to-noise ratio at an appropriate exposure level.

It is concluded from the effects described above that the biometricauthentication device 21 of this embodiment is capable of executingbiometric authentication with high precision.

Second Embodiment

The biometric authentication device 21 of a second embodiment of thisinvention executes biometric authentication based on images that areobtained by performing actual shooting twice.

The biometric authentication device 21 of the second embodiment has thesame structure as the biometric authentication device structure (FIG. 1)of the first embodiment. A detailed description on the structure istherefore omitted here. Authentication processing that is executed bythe biometric authentication device 21 of the second embodiment is thesame as the authentication processing (FIG. 7) executed by the biometricauthentication device 21 of the first embodiment, except Steps S8 andS9. Descriptions on the same processing steps are therefore omittedhere.

FIG. 18 is an explanatory diagram of an actual shooting mask image A,which is displayed on the biometric authentication device 21 infirst-time actual shooting according to the second embodiment of thisinvention. FIG. 19 is an explanatory diagram of an actual shooting maskimage B, which is displayed on the biometric authentication device 21 insecond-time actual shooting according to the second embodiment of thisinvention.

The biometric authentication device 21 in this embodiment executesactual shooting twice. In the first-time actual shooting, the biometricauthentication device 21 displays the actual shooting mask image A. Inthe second-time actual shooting, the biometric authentication device 21displays the actual shooting mask image B.

The actual shooting mask image A contains a mask region 190 and anirradiation region 191. The actual shooting mask image B contains a maskregion 192 and an irradiation region 193. The mask regions 190 and 192are regions that are displayed black by the liquid crystal on thedisplay screen. The irradiation regions 191 and 193 are regions in whichthe subject 1 is irradiated with light, and correspond to other regionsthan the mask regions 190 and 192.

The mask region 190 contained in the actual shooting mask image Acontains a region slightly larger than the right half of a region insidethe outline 40 of the subject 1. The mask region 192 contained in theactual shooting mask image B contains a region slightly larger than theleft half of a region inside the outline 40 of the subject 1.

The biometric authentication device 21 of the second embodimentcomposites an image obtained through the first-time actual shooting andan image obtained through the second-time actual shooting. In this way,the biometric authentication device 21 of the second embodiment obtainsa composite image containing the pattern of the blood vessels 2 near theoutline 40 of the subject 1. As a result, the biometric authenticationdevice 21 of the second embodiment can execute biometric authenticationwith higher precision than the biometric authentication device of thefirst embodiment.

FIG. 20 is an explanatory diagram of the positional relation between theactual shooting mask image A and the actual shooting mask image Baccording to the second embodiment of this invention.

In this explanatory diagram, the actual shooting mask image A and theactual shooting mask image B overlap with each other. As can be seen inthis explanatory diagram, an overlapping mask region 200 is providedbetween the actual shooting mask image A and the actual shooting maskimage B. The overlapping mask region 200 is a region in which the maskregion 190 contained in the actual shooting mask image A and the maskregion 192 contained in the actual shooting mask image B overlap witheach other. Accordingly, in the overlapping mask region 200, an image ofthe subject 1 is picked up redundantly in the first-time actual shootingand the second-time actual shooting.

The picked up images have a problem in that the pixel value rises aroundborders between the mask regions 190 and 192 and the irradiation regions191 and 193. The cause of this problem is scattered light which isgenerated in the process of the transmission of infrared light throughthe sensor board 4, and strays into the vicinity of the borders betweenthe mask regions 190 and 192 and the irradiation regions 191 and 193 andis measured accidentally.

To solve this problem, the biometric authentication device 21 compositesan image obtained through the first-time actual shooting and an imageobtained through the second-time actual shooting after removing data ofthe vicinity of the borders between the mask regions 190 and 192 and theirradiation regions 191 and 193. The discontinuity in pixel value in acomposite image is reduced in this manner.

In short, the overlapping mask region 200 is provided in order toprevent the removal of data of the vicinity of the borders from creatingan unphotographed region in a composite image.

FIG. 21 is a flow chart of authentication processing that is executed bythe biometric authentication device 21 according to the secondembodiment of this invention.

Steps shown in broken line in this flow chart indicate screen imagesdisplayed on the liquid crystal display board 5. The screen imagedisplayed on the liquid crystal display board 5 is kept displayed untilit is changed to the next screen image.

The biometric authentication device 21 first executes Steps S1 to S7.Steps S1 to S7 are the same as those in the authentication processing(FIG. 7) of the first embodiment, and descriptions thereof are omittedhere.

After creating a mask image in Step S7, the biometric authenticationdevice 21 executes actual shooting mask image creating processing (V1).In the actual shooting mask image creating processing, the biometricauthentication device 21 creates, from the created mask image, theactual shooting mask image A and the actual shooting mask image B.Details of the actual shooting mask image creating processing will bedescribed with reference to FIG. 22.

The biometric authentication device 21 next performs the display grayscale setting processing (FIG. 12) of the actual shooting mask image A(V2). Through this processing, the biometric authentication device 21displays the created actual shooting mask image A on the liquid crystaldisplay board 5 (V7). The liquid crystal gray scale D calculated in StepU5 of the display gray scale setting processing is set to theirradiation region 191 of the displayed actual shooting mask image A. Atthis point, the biometric authentication device 21 turns the display LED7 off and turns the detection LED 8 on. The biometric authenticationdevice 21 then executes the first-time actual shooting (V3).

The biometric authentication device 21 next performs the display grayscale setting processing (FIG. 12) of the actual shooting mask image B(V4). Through this processing, the biometric authentication device 21displays the created actual shooting mask image B on the liquid crystaldisplay board 5 (V8). The liquid crystal gray scale D calculated in StepU5 of the display gray scale setting processing is set to theirradiation region 193 of the displayed actual shooting mask image B. Atthis point, the biometric authentication device 21 turns the display LED7 off and turns the detection LED 8 on. The biometric authenticationdevice 21 then executes the second-time actual shooting (V5).

The biometric authentication device 21 composites an image obtainedthrough the first-time actual shooting and an image obtained through thesecond-time actual shooting (V6). The biometric authentication device 21thus obtains a composite image containing the pattern of the bloodvessels 2.

Thereafter, the biometric authentication device 21 executes Steps S10and S11. Steps S10 and S11 are the same as those in the authenticationprocessing (FIG. 7) of the first embodiment, and descriptions thereofare omitted here. The biometric authentication device 21 then ends theauthentication processing.

FIG. 22 is a flow chart of the actual shooting mask image creatingprocessing according to the second embodiment of this invention.

The actual shooting mask image creating processing is executed in StepV1 of the authentication processing (FIG. 21).

In FIG. 22, x represents the position in the X axis direction and yrepresents the position in the Y axis direction. N_(x) represents thepixel count in the X axis direction of a mask image, and N_(y)represents the pixel count in the Y axis direction of the mask image.The position of a pixel contained in the mask image is indicated by(x_(i), y_(j)), where i is 1 to N_(x) and j is 1 to N_(y).

After creating a mask image (FIG. 4) in Step S7, the biometricauthentication device 21 sets “1” to the currently processed point y_(j)in the Y axis direction (W1). The biometric authentication device 21next determines whether or not the currently processed point y_(j) isthe same as a value obtained by adding “1” to N_(y) (W2).

When the currently processed point y_(j) is the same as a value obtainedby adding “1” to N_(y), it means that every point in the Y axisdirection has been processed. Then, the biometric authentication device21 ends the actual shooting mask image creating processing and proceedsto Step V2 of the authentication processing (FIG. 21).

When the currently processed position y_(j) differs from a valueobtained by adding “1” to N_(y), on the other hand, it means that somepoints in the Y axis direction have not been processed yet. Then, thebiometric authentication device 21 identifies border points x_(ai) andx_(bi) between the irradiation region 41 and the mask region 42 at thecurrently processed point y_(j) in the mask image created in Step S7(W3). Here, the border point x_(bi) is larger than the border pointx_(ai). Specifically, the biometric authentication device 21 identifiestwo points at which a rapid change in pixel value of the currentlyprocessed point y_(j) is observed as the border points x_(ai) andx_(bi).

From the identified border points x_(ai) and x_(bi), the biometricauthentication device 21 calculates a central point x_(ci) in the maskregion 42 at the currently processed point y_(j) (W4). Specifically, thebiometric authentication device 21 calculates the central point x_(ci)using the following Mathematical Expression (5):x _(ci)=(x _(ai) +x _(bi))/2  (5)

The biometric authentication device 21 calculates from the obtainedcentral point x_(ci) a border point x_(Ai) between the irradiationregion 191 and the mask region 190 at the currently processed pointy_(j) of the actual shooting mask image A. Specifically, the biometricauthentication device 21 calculates the border point x_(Ai) using thefollowing Mathematical Expression (6):x _(Ai) =x _(ci) −x _(h)  (6)

The symbol x_(h) represents a value obtained by dividing the width inthe X axis direction of the overlapping mask region 200 (see FIG. 20) atthe currently processed point y_(j) by “2”, and is set in advance.

The biometric authentication device 21 next calculates from the obtainedcentral point x_(ci) a border point x_(Bi) between the irradiationregion 193 and the mask region 192 at the currently processed pointy_(j) of the actual shooting mask image B (W5). Specifically, thebiometric authentication device 21 calculates the border point x_(Bi)using the following Mathematical Expression (7):x _(Bi) =x _(ci) +x _(h)  (7)

Next, the biometric authentication device 21 determines whether or notthe border point x_(Ai) calculated in Step W5 is smaller than the borderpoint x_(ai) identified in Step W3 (W6).

When the border point x_(Ai) is equal to or larger than the border pointx_(ai), the border point x_(Ai) is inside the outline 40 of the subject1. The biometric authentication device 21 therefore proceeds directly toStep W7.

When the border point x_(Ai) is smaller than the border point x_(ai), onthe other hand, the border point x_(Ai) is outside the outline 40 of thesubject 1. The biometric authentication device 21 therefore sets theborder point x_(Ai) between the irradiation region 191 and the maskregion 190 at the currently processed point y_(j) of the actual shootingmask image A to the border point x_(ai) identified in Step W3 (W9).

Next, the biometric authentication device 21 determines whether or notthe border point x_(Bi) calculated in Step W5 is larger than the borderpoint x_(bi) identified in Step W3 (W7).

When the border point x_(Bi) is equal to or smaller than the borderpoint x_(bi), the border point x_(Bi) is inside the outline 40 of thesubject 1. The biometric authentication device 21 therefore proceedsdirectly to Step W8.

When the border point x_(Bi) is larger than the border point x_(bi), onthe other hand, the border point x_(Bi) is outside the outline 40 of thesubject 1. The biometric authentication device 21 therefore sets theborder point x_(Bi) between the irradiation region 193 and the maskregion 192 at the currently processed point y_(j) of the actual shootingmask image B to the border point x_(bi) identified in Step W3 (W10).

In this manner, the biometric authentication device 21 determines theborder point x_(Ai) of the actual shooting mask image A and the borderpoint x_(Bi) of the actual shooting mask image B at the currentlyprocessed point y_(j).

The biometric authentication device 21 next adds “1” to the currentlyprocessed point y_(j) (W8) and returns to Step W2.

As has been described, the biometric authentication device 21 of thesecond embodiment performs actual shooting twice using two mask imagesthat contain mask regions different from each other. The biometricauthentication device 21 composites images obtained through the actualshooting performed twice. As a result, the biometric authenticationdevice 21 obtains a composite image that contains the pattern of theblood vessels 2 throughout the entire region inside the outline 40 ofthe subject 1. The biometric authentication device 21 is thus capable ofexecuting biometric authentication with high precision.

Third Embodiment

The biometric authentication device 21 of a third embodiment of thisinvention uses a transmissive mask image in actual shooting.

The biometric authentication device 21 of the third embodiment has thesame structure as the biometric authentication device structure (FIG. 1)of the first embodiment. A detailed description on the structure istherefore omitted here. Authentication processing that is executed bythe biometric authentication device 21 of the third embodiment is thesame as the authentication processing (FIG. 7) executed by the biometricauthentication device 21 of the first embodiment, except Steps S7 andS8. Descriptions on the same processing steps are therefore omittedhere.

FIG. 23 is an explanatory diagram of a transmissive mask image 230,which is displayed on the biometric authentication device 21 when thesubject 1 is photographed according to the third embodiment of thisinvention.

All regions in the transmissive mask image 230 are translucent toinfrared light. The biometric authentication device 21 adjusts theliquid crystal gray scale of the transmissive mask image 230 using amethod that will be described later with reference to FIG. 24. Thebiometric authentication device 21 thus removes a back trend componentcontained in a picked up image, which enables the biometricauthentication device 21 to match the signal level of the pattern of theblood vessels 2 to the dynamic range of the sensor board 4. Thebiometric authentication device 21 can therefore obtain a picked upimage of high contrast-to-noise ratio and is consequently capable ofexecuting biometric authentication with high precision.

FIG. 24 is a flow chart of authentication processing that is executed bythe biometric authentication device 21 according to the third embodimentof this invention.

A step shown in broken line in this flow chart indicates a screen imagedisplayed on the liquid crystal display board 5. A screen imagedisplayed on the liquid crystal display board 5 is kept displayed untilit is changed to the next screen image.

The biometric authentication device 21 first executes Steps S1 to S6.Steps S1 to S6 are the same as those in the authentication processing(FIG. 7) of the first embodiment, and descriptions thereof are omittedhere.

Detecting the subject 1 in Step S6, the biometric authentication device21 sets “1” to a count m (R1). The count m indicates the number of timespreliminary shooting has been executed. The biometric authenticationdevice 21 next determines whether or not the count m is the same as avalue obtained by adding “1” to a scheduled preliminary shootingexecution count M (R2). The scheduled preliminary shooting executioncount M is the number of times preliminary shooting should be executedprior to actual shooting, and is set in advance. A typical value of thescheduled preliminary shooting execution count M is “3”.

When the count m is the same as a value obtained by adding “1” to thescheduled preliminary shooting execution count M, the biometricauthentication device 21 ends preliminary shooting and moves on toactual shooting. Then, the biometric authentication device 21 executesSteps S9 to S11. Steps S9 to S11 are the same as those in theauthentication processing (FIG. 7) of the first embodiment, anddescriptions thereof are omitted here. The biometric authenticationdevice 21 thereafter ends the authentication processing.

When the count m differs from a value obtained by adding “1” to thescheduled preliminary shooting execution count M, the biometricauthentication device 21 determines whether or not the count m is “1”(R3).

When the count m is “1”, the biometric authentication device 21 sets theinitial value D₀ to the liquid crystal gray scale D₁ of every pixel thatis contained in the transmissive mask image 230 used in the first-timepreliminary shooting (R10). The biometric authentication device 21 thenproceeds to Step R6.

When the count m is not “1”, on the other hand, the biometricauthentication device 21 executes a low pass filter (LPF) algorithm onan image P_(m-1), which is obtained through the preliminary shootingperformed last time (R4). The biometric authentication device 21 thusobtains a back trend component P′_(m-1) of an image obtained through thelast preliminary shooting. The LPF algorithm is processing of removing ahigh frequency component that corresponds to the pattern of the bloodvessels 2 from an image and extracting the back trend component P′_(m-1)alone. The LPF algorithm uses a digital filter or other knowntechnologies.

Next, the biometric authentication device 21 uses the followingMathematical Expression (8) to calculate a liquid crystal display grayscale D_(m) for each pixel that is contained in the transmissive mask230 used in the m-th run of preliminary shooting (R5):D _(m) =D _(m-1) ×P′ _(m-1) /P ₀  (8)

P₀ is an objective value of a back trend component P′ of an imageobtained through actual shooting, and is set in advance.

The biometric authentication device 21 next displays on the liquidcrystal display board 5 the transmissive mask image 230 used in the m-thrun of preliminary shooting (R9). The liquid crystal gray scale D_(m)calculated in Step R5 is set to each pixel contained in the displayedtransmissive mask image 230 (R6). At this point, the biometricauthentication device 21 turns the display LED 7 off and turns thedetection LED 8 on.

The biometric authentication device 21 then executes the m-thpreliminary shooting (R7), to thereby obtain an image P_(m).

The biometric authentication device 21 subsequently adds “1” to thecount m (R8) and returns to Step R2.

As described above, the biometric authentication device 21 removes aback trend component from a picked up image by displaying thetransmissive mask image 230 at a liquid crystal gray scale calculated byMathematical Expression (8).

Infrared light irradiating the subject 1 is detected after beingscattered within the subject 1. The relation between the irradiatinginfrared light and the detected infrared light is accordingly expressedby a point spread function. In addition, this point spread functionvaries depending on the location of the subject 1. Therefore, even whenthe liquid crystal gray scale of the transmissive mask image 230 isadjusted using Mathematical Expression (8), the biometric authenticationdevice 21 cannot remove a back trend component completely by performingpreliminary shooting only once. The biometric authentication device 21repeats preliminary shooting several times in order to improve thedegree of removal of the back trend component.

After the liquid crystal gray scale of the transmissive mask image 230is made closer to an appropriate value through repeated preliminaryshooting, the biometric authentication device 21 executes actualshooting using this transmissive mask image 230. This enables thebiometric authentication device 21 to match the signal level of thepattern of the blood vessels 2 to the dynamic range of the sensor board4. The biometric authentication device 21 can therefore obtain a pickedup image of high contrast-to-noise ratio and is consequently capable ofexecuting biometric authentication with high precision.

The biometric authentication device 21 also adjusts the liquid crystalgray scale for each pixel contained in the transmissive mask image 230.The biometric authentication device 21 can thus reduce darknessunevenness in a picked up image and is consequently capable of executingbiometric authentication with high precision.

The biometric authentication device 21, which is mounted to a cellularphone in the first to third embodiments, may be installed in any deviceor machine that includes a liquid crystal screen, such as a digitalcamera, an electronic organizer, a notebook computer, an automobile, andan ATM at a bank.

1. A biometric authentication device for identifying an individual whois associated with a subject based on a biometric pattern of the subjectwhich is included in a picked up image, comprising: a light guiding unitfor outputting, from a surface thereof, light incident on an end facethereof; a liquid crystal display unit for adjusting, on a display pixelbasis, an intensity of light output from the surface of the lightguiding unit, and then outputting the light in a direction of thesubject; an image pickup unit for picking up an image of the subject; adisplay light source for emitting light used as a backlight of theliquid crystal display unit such that the light is incident on the endface of the light guiding unit; a detection light source for emittinglight for irradiating the subject such that the light is incident on theend face of the light guiding unit; and a control unit for controllingprocessing of the biometric authentication device, wherein: the controlunit turns on the detection light when the image pickup unit picks up afirst image, which is used for authentication; the control unit turns onthe display light source when the liquid crystal display unit displaysinformation; the control unit creates a mask image including anon-irradiation region, which blocks the light output from the lightguiding unit, and an irradiation region, which transmits the lightoutput from the light guiding unit, according to a placement location ofthe subject; when the image pickup unit picks up the first image, theliquid crystal display unit displays the created mask image; the imagepickup unit picks up a fourth image when the detection light source islit and the liquid crystal display unit displays the created mask image;and based on the picked up fourth image, the control unit determines adisplay darkness of the liquid crystal display unit in the irradiationregion included in the created mask image.
 2. The biometricauthentication device according to claim 1, wherein the light guidingunit, the liquid crystal display unit, and the image pickup unit areoverlaid in order from inside the biometric authentication device. 3.The biometric authentication device according to claim 1, wherein: theimage pickup unit picks up a second image when both of the display lightsource and the detection light source are not lit; the image pickup unitpicks up a third image when at least one of the display light source andthe detection light source is lit; the control unit calculates adifferential between the picked up second image and the picked up thirdimage; and the control unit identifies the placement location of thesubject based on the calculated differential.
 4. The biometricauthentication device according to claim 1, wherein: the control unitcreates a plurality of the mask images according to the placementlocation of the subject; the image pickup unit picks up the first imageeach time the liquid crystal display unit displays one mask image out ofthe plurality of created mask images; and the control unit identifies anindividual who is associated with the subject based on a plurality ofthe picked up first images.
 5. The biometric authentication deviceaccording to claim 4, wherein non-irradiation regions included in theplurality of created mask images partially overlap with one another. 6.The biometric authentication device according to claim 1, wherein: theimage pickup unit picks up a fifth image when the detection light sourceis lit; the control unit creates a background image by removing highfrequency component information from the picked up fifth image; and thecontrol unit determines a display darkness of the liquid crystal displayunit on a display pixel basis in a manner that makes a pixel value ofthe created background image closer to a predetermined value.
 7. Thebiometric authentication device according to claim 1, wherein thebiometric pattern is a blood vessel pattern.
 8. The biometricauthentication device according to claim 1, wherein the display lightsource and the detection light source are composed of a common lightsource.
 9. A portable terminal provided with a biometric authenticationdevice for identifying an individual who is associated with a subjectbased on a biometric pattern of the subject which is included in apicked up image, comprising: a light guiding unit for outputting, from asurface thereof, light incident on an end face thereof; a liquid crystaldisplay unit for adjusting, on a display pixel basis, an intensity oflight output from the surface of the light guiding unit, and thenoutputting the light in a direction of the subject; an image pickup unitfor picking up an image of the subject; a display light source foremitting light used as a backlight of the liquid crystal display unitsuch that the light is incident on the end face of the light guidingunit; a detection light source for emitting light for irradiating thesubject such that the light is incident on the end face of the lightguiding unit; and a control unit for controlling processing of thebiometric authentication device, wherein: the control unit turns on thedetection light when the image pickup unit picks up a first image, whichis used for authentication; the control unit turns on the display lightsource when the liquid crystal display unit displays information; thecontrol unit creates a mask image including a non-irradiation region,which blocks the light output from the light guiding unit, and anirradiation region, which transmits the light output from the lightguiding unit, according to a placement location of the subject; when theimage pickup unit picks up the first image, the liquid crystal displayunit displays the created mask image; the image pickup unit picks up afourth image when the detection light source is lit and the liquidcrystal display unit displays the created mask image; and based on thepicked up fourth image, the control unit determines a display darknessof the liquid crystal display unit in the irradiation region included inthe created mask image.